1. Field of the Invention
This invention is directed to an article of manufacture and to a method. More specifically, this invention is directed to a muffler for effective suppression of environmentally offensive noise and the use thereof in noise reduction, without undue back pressure and impairment in engine performance. By design, this muffler is uniquely equipped for use in conjunction with a pre-cooled exhaust gas stream having a high cooling fluid content, such as typically produced by in-board marine engines. This invention is further directed to a method for noise suppression of moisture laden exhaust gases from in-board marine engines and other internal combustion engines having comparable exhaust streams.
2. Description of the Prior Art
At the outset, it essential to differentiate between the various types of internal combustion engines which, as a natural consequence of their operation, produce both exhaust gases and associated exhaust noise. The internal combustion engine associated with most forms of piston engines used in ground and aircraft conveyance have their respective engines confined and isolated from the passenger in a compartment which is relatively freely cooled and vented by the ambient air which passes over the conveyance during its movement through the (cooling) air. Moreover, ground and aircraft conveyance design generally readily accommodate engine, muffler and exhaust pipe set-ups which further contribute to the isolation and cooling of the exhaust gases without contact or exposure of either heat sensitive components of the conveyance, or the passenger, to either the heat from the exhaust or the exhaust system.
Conversely, in marine, industrial and emergency electrical generator systems, the exhaust system is not generally capable of isolation to the same degree describe above and, accordingly, the amount of heat given off by the exhaust system can create potential hazards to the both surrounding structure and occupants of such structures. Moreover, since the exhaust system is generally isolated from the movement of the circulating air, it requires some pre-cooling before it is exhausted. Thus, it is generally accepted practice to inject a cooling fluid, such as fresh or raw water into the exhaust manifold to lower the temperature of the exhaust gas before it passes through the engine pipe, muffler and exhaust (tail) pipe. The amount of water required to effect such pre-cooling is substantially in excess of that found in the ambient environment, and the muffler and exhaust system associated therewith must be specially designed to accommodate this "wet" exhaust gas stream.
Review of the patent literature has, for the most part, shown little, if any appreciation of the unique requirements of the exhaust systems associated with "wet" exhaust gas streams, notwithstanding differences in kind of the fluid handling problems associated with a dry versus a wet gas and the relative noise production & suppression problems associated with each. The patent literature does in point of fact disclose various muffler and catalytic converter configurations reportedly suitable for use on traditional internal combustion engines found in the automotive and piston powered aircraft. These patents which are described hereinafter, are discussed for the limited purpose of pointing out how dry exhaust gas systems are configured; and, such discussion is neither intended, nor should it be implied, to acknowledge either the equivalency of a wet and dry exhaust gas or that their respective exhaust systems function in the same or in a comparable manner. U.S. Pat. No. 2,946,651 (to Houdry) describes the catalytic treatment of a gas stream containing an oxidizable impurity (e.g. hydrocarbon). In brief, Houdry contacts the gas stream with an oxidation catalyst at high temperature to effect essentially complete combustion thereof. The device used by Houdry in his process consists of a thermally insulated housing containing a gas permeable bed which functions both as heat exchanger and as a heat generator. The oxidation catalyst in Houdry is maintained on a bed of dense refractory material and the gas is pre-heated to a temperature of about 1000 degrees Fahrenheit by the oxidation (combustion) of fuel contained (injected) in the waste stream. As such fuel is oxidized, the bed temperature is increased within the combustion chamber of the converter and the heat generated therein is transferred, (by a heat exchanger within the converter), to a second or gas processing area within the bed so as to maintain the temperature in this processing area at sufficient levels to effect essentially complete catalytic oxidation of the lower temperature gases. In summary, the Houdry treatment, and the associated equipment necessary for the implementation thereof, are typical of the configuration used in the processing of essentially "dry" gas streams containing unburned hydrocarbons.
U.S. Pat. No. 3,159,237 (to Thomas) described a muffler of relatively unique design and construction at the time his device was conceived. In one of the embodiments of his invention, the Thomas muffler uses a vesicular metal element contained within a housing as a replacement for the more traditional acoustical packs of copper, steel or glass wool. The vesicular sound deadening media described by Thomas for his acoustical pack can be either of "open" or "closed" cellular mass having an essentially solid, non-cellular skin or casing. The various configuration of the Thomas muffler utilizing such vesicular materials are illustrated in FIGS. 1-9 of his patent. In each such embodiment of his device a channel a gas inlet pipe introduces exhaust gas into the muffler where it contacts and passes through the vesicular mass and thereafter exists the muffler through an outlet pipe, which is either a continuation of the inlet or offset relative to the inlet. The muffler described by Thomas is typical of the design which can be utilized to deaden the sound produced by internal combustion engines and, accordingly, is competent to muffle the sound of "dry" exhaust gases.
U.S. Pat.No. 3,163,256 (to Lanning) describes the use of a ceramic honeycomb baffle in a muffler to deaden the sound produced by an internal combustion engine. The selection of a ceramic as the material of choice by Lanning is based upon the inventor's desire to produce a "resistive" type of muffler that was both strong and capable of withstanding high temperatures under chemically corrosive conditions. The materials of choice identified by Lanning appear at Column 3,lines 3-30, and include various refractory components that are compatible with ceramic fabrication methods and materials. The muffler described by Lanning is typical of the design which can be utilized to deaden the sound produced by internal combustion engines and, accordingly, is competent to muffle the sound of "dry" exhaust gases.
U.S. Pat. No. 3,495,950 (Barber et al ) describes a catalytic muffler for exhaust emission control. The disclosure of Barber which is of particular interest in the context of evaluation of Applicant's invention relates to the use of an air injection system to supplement the oxygen (unburned air) in the exhaust gases to effect more complete oxidation of the hydrocarbon residues thereof. More specifically, the Barber patent describes the custom and practice in design of catalytic conversion systems to inject pre-heated air into the exhaust stream to supply a supplemental quantity of oxygen to improve the efficiency of the catalytic conversion process. It is important to note the requirement of the designer of such system to pre-heat the injected air (so as not appreciably lower the temperature of the exhaust gases) is simply his acknowledgement of the criticality of temperature to the oxidation process and, thus, his desire to maintain catalytic converter temperatures as high as possible for effective oxidation of the hydrocarbon residues in the exhaust. The catalytic converter described by Barber is typical of the design which can be utilized to both chemically process such exhaust gases and deaden the sound produced by internal combustion engines. Accordingly, Barber's device is competent to muffle the sound of "dry" exhaust gases. U.S. Pat. No. 3,692,497 (to Keith et al) describes a catalytic converter for treatment of exhaust gases which incorporates unique internal modification to the converter housing to maintain the catalyst supporting element securely in place during use (treatment of exhaust gas). Apparently Keith and others had observed that the catalyst support can be physically displaced within the converter housing during the rigors encountered in service; and that such displacement can result in incomplete oxidation of exhaust gases which may by-pass the catalyst supporting element. This problem is resolved in the structure described by Keith in providing an inward extension of the converter housing which physically engages the catalyst supporting element and thereby maintains such element in place in the housing. The catalytic converter described by Keith is otherwise typical of the design which can be utilized to process exhaust gases produced by internal combustion engines and, accordingly, is competent to oxidize "dry" exhaust gases. U.S. Pat. No. 3,852,042 (to Wagner) describes describes a unique catalytic converter design wherein a pair of spaced, dome-shaped, perforated screens (positioned between the converter inlet and the catalyst bed) serve to dampen and modulate exhaust gas pollution which causes vibrational movement of the catalyst bed within the converter housing and, thus, minimize physical damage to such a relatively fragile bed. Wagner's converter design eliminates the above vibration by diffusing the incoming gases within the converter chamber. The catalytic converter described by Wagner is otherwise typical of the design which can be utilized to process exhaust gases produced by internal combustion engines and, accordingly, is competent to oxidize "dry" exhaust gases.
The foregoing patents have been described in chronological order based upon their date of issue. Accordingly, the reader should not attribute any relative weight, as to their pertinence on the patentability of the Applicant's invention, on such order of discussion. All of the foregoing simply describe what has come to be recognized as generally accepted alternative designs for the processing and muffling of "dry" exhaust gases. It is further particularly apparent that catalyst bed temperature is critical to effective oxidation of exhaust gases; and, that converter efficiency cannot tolerate the introduction of ambient temperature air without suffering a demonstrative reduction in converter performance. Accordingly, where supplemental air is introduced into the exhaust stream to supply supplemental oxygen, it must be pre-heated. Thus, the designs described for catalytic converters all contemplate the maintenance of extremely high bed temperatures.
By way of contrast, the use and operation of in-board engines (and internal combustion engines which are similarly confined) requires and contemplates the pre-cooling of the exhaust by liquid injection to protect both the immediate environment of the engine and persons in proximity to its operation. The traditional designs for both catalytic converters and mufflers are manifestly inadequate for sound dampening of "wet" exhaust gas streams due to their mandated low temperature of operation and the high fluid content of the "wet" exhaust which passes through the internal sound deadening elements that must be contained therein. Where an effort has been made to substitute the more traditional muffler (designed for automotive use) in the marine environment, its performance has been inadequate because of the unique and strenuous demands of a "wet" exhaust. Accordingly there is a continuing need to provide a muffler that can accommodate a "wet" exhaust, (such as present in cooling of in-board marine engines) without fouling from debris contained in the injected cooling water and yet provide the requisite sound deadening qualities.